The present invention relates to magnetic hard disk drives. More specifically, the present invention relates to a method of electrically coupling a flexible circuit assembly to a circuit board.
FIG. 1 provides an illustration of a typical disk drive. The typical disk drive has a head gimbal assembly (HGA) configured to read from and write to a magnetic hard disk 101. The HGA and the magnetic hard disk 101 are mounted to the base 102 of a main board 103. The disk 101 is rotated relative to the base 102 by a spindle motor 104. The HGA typically includes an actuator arm 105 and a load beam 106. The HGA supports and positions a magnetic read/write slider 107 above the magnetic hard disk 101. The slider may contain transducers to perform the read/write function. The HGA is rotated relative to the base 102 along the axis of a pivot bearing assembly 108 by an actuator frame 109. The actuator frame 109 contains an actuator coil 110 driven by a magnet 111. A relay flexible printed circuit 112 connects a board unit 113 to the transducer of the magnetic read/write slider 107. The signal from the transducer is transmitted along the relay flexible printed circuit 112 via a printed circuit board (PCB) 114 coupled to the frame 109.
The flexible printed circuit assembly 112 can be electrically coupled to the PCB 114 using a number of different methods. FIG. 2 provides an illustration of one method of electrically coupling the flexible circuit assembly 112 to the PCB 114 according to the prior art. A flexible substrate 201 of the flexible printed circuit assembly 112 is positioned above a circuit substrate 202 of the PCB 114. The circuit substrate 202 can be rigid or flexible. In this case, a bonding pad 203 is mounted on the circuit substrate 202 and electrically coupled to circuitry within the PCB 114. A connecting pad 204 is mounted on the flexible substrate 201 and electrically coupled to circuitry within the flexible circuit assembly 112. The bonding pad 203 and connecting pad 204 are aligned. Then, a soldering bump 205 is placed upon the bonding pad 203 and the connecting pad 204. The soldering bump 205 can have a copper core 206. A heated tip 207 is then used to reflow the solder bumps 205. The tip 207 can be heated using a laser or ultrasonic energy. The tip 207 presses the flexible substrate 201 against the circuit substrate 202 for a set period of time, and the heat from the tip 207 melts the opposing solder bumps 205 together to form a bond. The copper cores 206 come into contact creating an electrical connection.
FIG. 3 provides an illustration of an alternate method of electrically coupling the flexible circuit assembly 112 to the PCB 114 according to the prior art. The flexible substrate 201 of the flexible printed circuit assembly 112 is positioned above the circuit substrate 202 of the PCB 114. The bonding pad 203 is mounted on the circuit substrate 202 and electrically coupled to circuitry within the PCB 114. The connecting pad 204 is mounted on the flexible substrate 201 and electrically coupled to circuitry within the flexible circuit assembly 112. In this case, the bonding pad 203 and the connecting pad 204 are coated with gold. An anisotropic conductive film (ACF) is applied to the bonding pad 203. The bonding pad 203 and the connecting pad 204 are aligned. Then the heated tip 207 presses the flexible substrate 201 against the circuit substrate 202 for a set period of time. The heat from the tip 207 melts the ACF to the connecting pad 204 to form a bond.
The use of the laser-heated tip 207 requires a great deal of precision. Additionally the tools required in performing this method are also quite costly. The accuracy required in the alignment process also greatly reduces the efficiency of these bonding processes.